This invention relates to an apparatus and method for performing a predetermined process to samples (objects to be treated) having a microstructure such as semiconductor substrates and micromachines, and particularly to a processing apparatus and a processing method for performing a processing with use of a high-pressure fluid such as supercritical fluid, subcritical fluid or liquefied gas.
Recently, large-scaled integrated circuits have been formed on semiconductor substrates. As the integrated circuits have been formed at a larger scale, the line width of a circuit pattern to be formed on a semiconductor wafer has decreased to the order of submicron. As the line width is narrowed, capillary force is acted on the gas-liquid interface of the substrate wafer when the semiconductor wafer is dried under an atmospheric pressure after washing with a chemical. As a result, it is highly likely that the size of the pores and grooves in the semiconductor wafer may be reduced or cracks may be generated on the wafer surface.
A supercritical drying process has been proposed to eliminate the above drawbacks resulting from capillary force. The supercritical drying process is a process of drying semiconductor wafers with use of a supercritical fluid, namely, a fluid which has a property of a substantially interim state between gas phase and liquid phase and whose density is close to that of liquid and whose diffusion coefficient and viscosity are close to those of gas by allowing a material fluid) to exceed a critical point (critical temperature, critical pressure) inherent to the material. The supercritical drying process is free from generation of gas-liquid interface, and accordingly, semiconductor wafers can be dried without causing size reduction of the pores and grooves or generating cracks, which may result collapse of microstructures around the grooves. Japanese Unexamined Patent Publication No. HEI 11-87306 discloses an exemplified supercritical drying apparatus with use of a supercritical fluid. Japanese Unexamined Patent Publication No. HEI 10-125644 discloses a method for removing residual matters from the semiconductor substrate surfaces with use of a supercritical fluid (supercritical carbon dioxide). Japanese Unexamined Patent Publication No. SHO 60-192333 discloses a method for removing resist with use of a supercritical fluid or liquefied gas.
In a physically strict sense, there is no boundary region in a supercritical region. For instance, there is a high-pressure fluid exhibiting generally the same property as a supercritical fluid even at a temperature lower than a critical point. Such a fluid is called as a subcritical fluid. The subcritical fluid can be used in a predetermined process to eliminate the drawbacks resulting from capillary stress in the similar manner as a supercritical fluid.
Allowing a supercritical fluid or the like to flow (agitating a fluid) is effective in performing an efficient and uniform drying process onto substrates such as semiconductor wafers in a drying process with use of a supercritical fluid or the like. In view of this, Japanese Unexamined Patent Publication No. HEI 11-87306 discloses an agitating apparatus equipped with an agitating rotary mechanism having an agitating wing to agitate a fluid in a pressure vessel (processing chamber), and a substrate rotary mechanism for rotating a substrate in the pressure vessel.
The drying apparatus equipped with the agitating apparatus enables to perform an efficient and uniform drying process onto a substrate, but may likely to cause contamination of the substrate due to adhesion of particles and the like. It is a general practice in the drying apparatus equipped with the agitating apparatus to provide a power source (e.g. motor) outside of the pressure vessel for driving the agitating apparatus so as to transmit a driving force of the power source to the interior of the vessel via a rotary shaft that has been sealed against a high pressure. In such an arrangement, dusts (particles) may be generated in the sealed portion of the rotary shaft due to abrasion of the rotary shaft, which may likely to intrude into the vessel. There is an idea of providing a power source inside a pressure vessel to omit the sealed portion of the rotary shaft. In such a case, a rotary portion of the agitating wing and many of the parts which may likely to cause metal contamination are arranged inside the pressure vessel thus resulting in contamination of substrates.
As mentioned above, none of the above techniques is satisfactory in production of semiconductor substrates and the like which requires strict control on preventing contamination of the substrates with particles and other foreign matters. There has been a demand for an apparatus and method which can solve the above drawbacks.
There is another idea of implementing a series of processes from a chemical treating process to a drying process in a high-pressure vessel (chamber) in the aforementioned supercritical processing apparatus (high-pressure processing apparatus). According to this technique, a substrate is transported to a pressure vessel of the supercritical processing apparatus, treated with a variety of chemicals by being supplied with the chemicals one after another, and dried by a supercritical fluid.
In the above apparatus, the pressure vessel and pipes connected thereto are generally made of a metallic material in light of the fact that a high pressure fluid (supercritical fluid) is used. Some of the chemicals used in the chemical treatment have a property of corroding a metal. Accordingly, there should be considered a problem relating to corrosion, e.g., a problem that particles and the like may be generated.
In order to solve the above problems, Japanese Unexamined Patent Publication No. SHO 64-45125 discloses an idea of coating the parts which is likely to be corroded with a corrosion-resistive agent (made of e.g. quartz or fluoroethylene resin), and Japanese Unexamined Patent Publication No. SHO 63-221803 discloses an idea of applying a corrosion-resistive lining.
It is necessary to apply the corrosion-resistive agent to the pipes connected to the pressure: vessel as well as to the pressure vessel (processing chamber). However, it is technically difficult to apply a corrosion-resistive agent to the pipes having a small diameter and a long length. Also, some of the corrosion-resistive agents have inferior durability in high-pressure use. Accordingly, use of such agents having inferior durability is practically infeasible.
In view of the above, there has been a demand for solving the problems relating to corrosion in the supercritical processing apparatus.